1. Field of the Invention
This invention relates, generally to the art of prosthetics. More particularly, it relates to improvements in prosthetic feet.
2. Description of the Prior Art
During normal ambulation, the first part of a foot to contact the ground is the trailing end of the heel. This initial contact between heel and ground is known as the xe2x80x9cheel strike.xe2x80x9d The trailing end of the heel is soft and thus cushions the heel strike to at least some extent. The hard bottom of the heel is the next part of the foot to strike the ground; its hardness allows it to support the entire weight of the body. The foot continues to rotate in the well-known way until the toes xe2x80x9cpush offxe2x80x9d at the end of a step.
Early prosthetic feet are quite rigid and provide little or no cushion to the impact on the ground at the moment of xe2x80x9cheel strikexe2x80x9d and little or no elastic response at xe2x80x9cpush off.xe2x80x9d The shock of impact is thus transmitted directly to the skeletal structure of the user, and the lack of elastic response forces an unnatural gait.
Perhaps the earliest prosthetic foot that provides an elastic response at heel strike and push off is disclosed in U.S. Pat. No. 4,547,913 to Phillips, assigned to Flex Foot, Inc. Multiple versions of that device have been developed. The original version is formed of a carbon fiber-epoxy matrix consisting of a one-piece combination pylon upper and a one-piece sole. Mechanical fasteners interconnect the upper and the sole. In a second embodiment, the pylon is a round hollow tube and is connected by mechanical fasteners to a rectangular-shaped upper. A third version is like the first except that a standard Sach(copyright) foot adapter is employed to connect a standard prosthetic pylon. A fourth version is like the third but has a slightly different geometry. In a fifth version, an elastomeric glue connects the upper and the sole. In additional embodiments, leaf springs or hydraulic cylinders are incorporated into the prosthetic foot.
Although the developments in the art since the mid 1980s have significantly advanced the technology of prosthetic feet, the known prosthetic feet still provide little or no heel elasticity in a direction parallel to the ground. Instead, they provide elastic response in a vertical plane. Thus, although the impact at heel strike is reduced vis a vis the pre-1980""s prosthetic feet, the reduced impact is transmitted vertically to the skeletal structure of the user, and the elastic response in a vertical plane causes a four to six millimeter bounce at heel strike. This vertical response causes an unnatural walk because a healthy human heel is soft at the trailing end where heel strike occurs and is hard on the bottom so that it can support the entire weight of the body. Thus, the normal gait of a human includes a rolling motion as the tailing end of the heel strikes the ground; there is no vertical motion causing the heel to bounce upon ground impact.
Accordingly, there is a need for a prosthetic foot that provides substantial heel elasticity in a direction parallel to the ground.
A healthy human foot rolls on the lateral part of the foot during ambulation. The medial part of the foot provides a cushion and the force required at push off. Thus, there is a smooth transition from heel strike to push off, with no vertical dynamic response of the type that could cause the foot to bounce. Prosthetic feet of the type heretofore known, however, do not provide a smooth transition from heel strike to push off. This lack of a smooth transition produces what is known in the industry as a xe2x80x9cflat spot.xe2x80x9d The presence of a flat spot between heel strike and push off produces an unnatural gait.
More particularly, the dynamic response is primarily vertical at the heel and the toe of a prosthetic foot. There is little or no component of the dynamic response in a horizontal plane as present in a healthy natural foot. The absence of dynamic response in a horizontal plane results in a step like motion going from an elastic vertical motion at heel strike to little or no support at mid-stance (the flat spot), and then again to an elastic vertical motion at push off.
There is a need, therefore, for a prosthetic foot having a dynamic response in a horizontal plane during heel strike, that provides a smooth transition between heel strike and push off to eliminate the flat spot, and that provides a dynamic response in a horizontal plane during push off.
The human foot provides a more rigid support laterally than medially. This design is advantageous because when an instability occurs, the weight of the person shifts from the rigid outer or lateral edge of the foot to the less rigid inner or medial edge. In this way, the prosthetic foot takes advantage of the presence of the natural foot, i.e., the lateral-to-medial motion experienced at the moment of an instability shifts additional support duties to the natural foot. One major drawback of the heretofore known prosthetic feet is the fact that such feet provide an exactly vertical response during ambulation with no component toward the medial section of the foot. Thus, if an instability in one foot urges the person to fall away from the natural foot, there is no shift of weight toward the medial part of the prosthetic foot as would occur in a natural foot, and the likelihood of a fall is substantially increased.
A prosthetic foot is therefore needed that has differentiated medial and lateral stiffness so that it can respond to instabilities in much the same way as a natural foot.
However, in view of the prior art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how the identified needs could be fulfilled.
The long-standing but heretofore unfulfilled need for an improved dynamic prosthetic foot is now met by a new, useful, and nonobvious dynamic prosthetic foot having a split upper ankle and a heel with differentiated elasticity. The novel prosthetic foot includes a sole, a lateral heel, and a medial heel. A lateral ankle part separates from said sole along a transverse parting line and includes a gradual upward bend, a horizontal part, and a vertically extending part. The vertically extending part providing a lateral pylon support. A lateral pylon connector is secured to the lateral pylon support on a trailing side thereof. The transverse parting line is approximately halfway between a leading end of the sole and a trailing end of the medial heel.
The lateral heel has a leading part that underlies and supports the horizontal part of the ankle part and a return bend is formed in a trailing end of the lateral heel. The return bend has a radius of curvature and terminates in a free leading end that is angled slightly upwardly relative to a horizontal plane so that a convexity near the free end is adapted to be in abutting engagement with a support surface during ambulation.
A medial heel extension is formed integrally with the sole and separates from the lateral ankle part along the transverse parting line. The medial heel extension includes a medial heel formed integrally with the medial heel extension and is adapted to abut the support surface during ambulation. The medial heel has a return bend formed therein, a horizontal part, and a vertically extending part formed integrally with the horizontal part. The vertically extending part of the medial heel provides a medial pylon support. A medial pylon connector is secured to the medial pylon support on a trailing side thereof. The medial heel has a trailing end that trails the trailing end of the lateral heel.
The lateral heel and the medial heel provide differentiated elastic responses to impact forces created by ambulation.
The horizontal part of the lateral ankle part and the horizontal part of the medial heel are co-planar with one another.
A concavity is formed about mid-length of the sole to perform the function of an arch of a natural foot. A convexity is formed about mid-way between the concavity and a toe end of the prosthetic foot. The convexity performs the function of a ball of a natural foot.
In a second embodiment, the lateral and medial pylon supports and pylon connectors are supplanted by elongate lateral and medial pylons that are about twenty inches (20xe2x80x3) in length. A prosthetist cuts the pylons as needed when fitting the novel foot to a prosthetic socket.
The elongate lateral and medial pylons are laminated at respective uppermost ends thereof to a prosthetic socket or are connected at respective uppermost ends thereof to a connector member that is laminated to the prosthetic socket.
Alternatively, the lateral and medial pylons are connected at respective uppermost ends thereof to a pyramid-receiving connector that engages a pyramid that depends from the prosthetic socket.
An important object of this invention is to provide a prosthetic foot having heel elasticity in a direction parallel to the ground.
Another important object is to provide a prosthetic foot having a smooth transition from heel strike to push off.
Yet another object is to provide a prosthetic foot having differentiated medial and lateral stiffness so that an instability tends to shift weight from the lateral edge of the prosthetic foot to the medial edge thereof, just as in a natural foot.
These and other important objects, advantages, and features of the invention will become clear as this description proceeds.
The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the description set forth hereinafter and the scope of the invention will be indicated in the claims.